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Supporting Information

The longest polyene

Muhammad Zeeshan,a Hans-Richard Sliwka,

a Vassilia Partali,

a Ana Martínez*

b

aDepartment of Chemistry, Norwegian University of Science and Technology, Trondheim, Norway.

E-mail: hrs@nvg.ntnu.no b Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de México, Circuito

Exterior s/n, Coyoacan 04510, Mexico,. E-mail: martina@iim.unam.mx

Scheme 1S. Selected compounds for C=C elongation. The year of synthesis demonstrates the

slow progress in C=C extension.

C4:2 Ref. 1. C6:3 van Romburgh, P.; van Dorsen, W. Proc. K. Akad. Wetensch. Amsterdam 1905, 8, 565; Perkin,

W.H. J. Chem. Soc. Trans 1907, 91, 806. C12:5 Ref. 2. C28:8 Ref. 4. C42:13, Ref. 5. C30:15 F. Sondheimer, R.

Wolovsky, Y.J. Amiel, Y. J. Amer. Chem. Soc. 1962, 84, 274. C22:11 Clar. E.; John, F. Chem. Ber. 1929, 62B,

3021. C36:18, Ref. 8. C60:19, Ref. 18. C167:23 Ref. 15.

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Experimental

Synthesis of C30diAld, C40diAld and C50diAld. An oven-dried microwave vial was

charged with phosphonium salt C5P (2588.6 mg, 5.06 mmol) and CH3OK (25%, 374

µL, 5.06 mmol) in dry MeOH (15 mL) and stirred at room temperature for 30 min.

C20diAld (100 mg, 0.33 mmol) dissolved in dry CH2Cl2 (5 mL) was added and the

mixture irradiated by microwaves for 20 min at 80 W and air-jet cooling to room

temperature (Paar Synthos 3000 Microwave reaction system). H2O (1 mL) was added

and the resulting mixture concentrated in vacuum. The residue was dissolved in

CH2Cl2 (30 mL), extracted with H2O (3 × 30 mL), the organic layer dried with

Na2SO4 and concentrated in vacuum. The residue was dissolved in CH2Cl2 (30 mL),

a crystal of p-toluenesulfonic acid was added and the solution stirred at room

temperature under N2 for 30 min. The reaction mixture was washed with 5% NaHCO3

(3 × 20 mL) and H2O (3 × 20 mL) and the organic phase dried with Na2SO4 and

concentrated in vacuous. The residue was purified by flash column chromatography

(toluene/acetone, 9.8:0.2). C30diAld reacted similarly with CP5 to C40diAld;

C40diAld reacted with CP5 to C50diAld. C30diAld: yield 90%, C40diald: yield

89%, C50diald: yield 77%. HRMS calcd. for C30H36O2 428.2714, found 428.2715;

C40H48O2 560.3651, found 560.3654; C50H60O2 692.4619, found 692.4593

Synthesis of C80Zea:27. An oven-dried microwave vial was charged with

phosphonium salt C15Zea-P (89.46 mg, 0.17 mmol). C50diAld (8.0 mg, 0.01

mmol), dissolved in a mixture of 1,2-epoxybutane and ethanol 1:3 (5 mL) by

refluxing for 30 min, was added and the mixture stirred at room temperature for 15

min following microwave irradiation for 20 min at 320 W with air-jet cooling to room

temperature. H2O was slowly added and the mixture stirred for 2 h. The precipitated

crystals were filtered and washed 3 times with cold EtOH/H2O 4:1 (10ml), yield: 7

mg, 63%. TLC eluent CHCl3: acetone 9.8: 0.2. HPLC (silica, CHCl3/acetone, 70:30)

showed the presence of C50diAld and a minor impurity. HRMS calcd. for C80H104O2

1096.8036 [M+H]+, found 1096.8014. Work-up procedures and characterization of

C80Zea were performed without specific precautions. 1H NMR (CDC13, 300 MHz): δ (ppm) = 6.11-6.95 (m, 38 H), 4.01 (m, 2 H), 2.40 (m,

2 H), 2.36 (m, 2 H), 1.99 (s, 36 H), 1.74 (br. s, 2 H), 1.54 (s, 2 H), 1.73 (s, 6 H), 1.09-

1.05 (s, 12 H). 13

C NMR (CDCl3, 125 MHz): δ (ppm) = 138.4, 137.7, 135.6, 131.1,

129.4, 126.1, 125.7, 65.1, 48.4, 42.5, 37.1, 30.2, 28.7, 24.7, 21.6, 12.6, 9.7. 1H-NMR and

13C-NMR spectra are similar to published data of C40Zea and similar

compounds (Englert, G. In Carotenoids Volume 1B: Spectroscopy; Britton, G.;

Liaaen-Jensen, S.; Pfander, H. Eds.; Birkhäuser: Basel, 1995, chpt. 6).

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1H NMR of C80-zeaxanthin

13C NMR of C80-zeaxanthin

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Figure 1S. Typical cis � trans isomerization experiment with C80Zea in CH2Cl2 using I2

and irradiation with a diffuse sun lamp (spectra taken in 5 min intervals). The spectral bands

are not affected by I2 and light, indicating the absence of cis-isomers. CH2Cl2 is the most

convenient compound solvent and although not appearing optimal for irradiation experiments

it was not affected by the experimental conditions (Pacaková, V.; Vojtêchova, H.; Coufal, P.

Chromatographia 1988, 25, 621)

Molecular calculation. DFT approximation in Gaussian03 was used for all

calculations at the KanBalam supercomputer (DGSCA-UNAM). Full geometry

optimization without symmetry constrains and frequency analysis was carried out for

all stationary points using B3LYP/D95V. Absorption spectra from the optimized

structures were computed in the gas phase and CH2Cl2 with TDDFT using the M06-

2X and 6-311g basis sets with the associated polarized continuum model.

Figure 2S. Calculated spectra in CH2Cl2 of 31,31'-cis-C80Zea …… (λmax = 580 nm) and all-

trans-C80Zea — (λmax = 672 nm). The calculated trans-spectrum displays absorption in the

lower wavelength part, similar to the measured spectrum. The calculation of the cis-

compound did not develop a cis-peak (Ref. 20).

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Calculation of the theoretical number of cis-isomers N for a symmetrical polyene

with an odd number of double bonds N. (L. Zechmeister, in Cis-trans isomeric

carotenoids, vitamins A, and arylpolyenes, Springer, Wien 1962, Chap. 2):

N = 2(N-1)/2

x (2(N-1)/2

+1)

For C80Zea:27 with 25 chain double bonds (ring double bonds not considered)

N = 2(25-1)/2

x (2(25-1)/2

+1) = 16 781 312.

Maximal 6-7% cis-isomers are expected according to Zechmeister, thus 6% of

N corresponds to 1 006 878.

The calculation is entirely hypothetical. Cis-isomers are not expected to occur in long

polyenes (Ref. 4, 21, 22).

HPLC (Nucleosil 100-5 silicalgel 5 µm, column 25 cm x4.6 mm): 3.97 m C80Zea

88.9%; 3.52 m C50diAld 8.8%; 3.09 m impurity 2.3%, eluent CHCl3/acetone 70:30.

The Vis spectrum recorded from the resolved main peak is identical to the spectrum

in Fig. 1.

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Vis-spectrum of C30diAld in CH2Cl2, λmax = 514 nm.

Vis-spectrum of C40diAld in CH2Cl2, λmax = 554 nm.

Vis-spectrum of C50diAld in CH2Cl2, λmax = 572 nm.